The present invention relates to aircraft radar systems, and more particularly to a multiple altitude radar system having the capability to operate both in front of an aircraft and at an angle below the aircraft for improved detection of weather patterns and associated turbulence.
Modern aircraft are equipped with many on-board safety and diagnostic systems, including a radar system for detecting weather patterns located generally in front of the aircraft. The first aircraft radar systems utilized parabolic antennas which had a radiation pattern including substantial side lobes, or areas outside the main antenna focusing region in which lesser intensities of radiation are emitted. At cruising altitudes, the side lobes of these radar systems would detect weather patterns located below the flight path altitude of the aircraft. Situations would occasionally occur in which the main beam of the radar system would not detect a region of weather having a high enough reflectivity to be displayed on the instrument display, but the side lobe of the radar system would detect a region of high reflectivity below the flight path of the aircraft and would thus generate a display on the instrument panel. These situations most often occurred when the cruising altitude of the aircraft was substantially above the freezing altitude. Pilots learned to use this type of information provided by the radar system to their advantage, relying on the lower side lobe of the radar system to detect regions of weather below the freezing altitude. If the pilot saw a cloud top and the radar system indicated detection of a weather pattern, the pilot knew that the weather pattern was located below the altitude of the aircraft flight path.
Parabolic antennas have been gradually replaced in nearly all modern aircraft radar systems by flat plate phased array antennas in an effort to reduce the cost and improve the performance of the radar systems. The flat plate phased array antenna has reduced side lobe radiation levels, which is desirable to reduce spurious radar detections outside of the main antenna lobe. However, this also results in the loss of the ability to detect weather patterns whose major regions of high radar reflectivity are located below the flight path of the aircraft. One attempted solution to this problem has been to increase the gain of the radar system, so that areas of moderate or relatively low radar reflectivity (e.g., the frozen top portion of a storm) would be detected and displayed on the instrument panel. This solution has not been entirely effective, since the radar reflectivity of the top portion of a storm is often so low that radar detection is impossible, and since storms may not even exist at the altitude of the aircraft flight path until the aircraft passes above the storm, while the storm may grow up to the level of the aircraft to intersect the flight path.
What is needed is a radar system that enables detection of weather patterns located below the altitude of an aircraft.
What is also needed is a radar system that detects developing weather patterns that are predicted to grow into the flight path of an aircraft.
The present invention is a multiple altitude radar system for an aircraft. The radar system performs a main radar sweep at an altitude of the aircraft and at least one secondary radar sweep at an angle from the altitude of the aircraft to a ground altitude. These multiple radar sweeps provide data that can then be analyzed and manipulated to determine weather locations in three dimensions. In some embodiments, more complex and complete weather information such as turbulence, storm growth rates, and the like may also be determined.